The Growing Significance of an Overlooked Atmospheric Chemical Reaction

  • 20 July 2021
The Growing Significance of an Overlooked Atmospheric Chemical Reaction

A new study funded by CPO’s Atmospheric Chemistry, Carbon Cycle, & Climate (AC4) program shows that what was once a small, overlooked chemical reaction might be increasingly important in a warming climate. 

Most chemical transport models leave out the process of atmospheric ammonia oxidation—when an ammonia molecule in the air changes into something new after reacting with oxygen—as it is a slow process that takes place over weeks. Scientists assume that other reactions take place long before ammonia oxidation occurs. This study, published in Earth and Space Chemistry, incorporates an explicit mechanism to simulate this left-out chemistry. 

Researchers from MIT and University of Toronto found that including ammonia oxidation does not significantly change how the models represent global ammonia concentrations. However, they did find that while including oxidation might not make a difference at the global scale, it could matter for specific regions. Their work showed small but significant changes in important greenhouse gases like ozone, particularly over the Indian subcontinent. 

The researchers also simulated future emission scenarios, which show that atmospheric oxidation of ammonia will become an increasingly important source of both nitrogen and nitrous oxide—a greenhouse gas that packs a larger punch than carbon dioxide. The chemical reaction could account for up to 21% of future nitrous oxide emissions. 

The study suggests that climate models focused on nitrous oxide emissions should explicitly include ammonia oxidation, though more work is needed to explore the early relationships revealed here. 

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